17O MAS NMR Correlation Spectroscopy at High Magnetic Fields

The structure of two protected amino acids, FMOC-L-leucine and FMOC-L-valine, and a dipeptide, N-acetyl-L-valyl-L-leucine (N-Ac-VL), were studied via one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy. Utilizing O-17 magic-angle spinning (MAS) NMR at multiple magnetic fields (17.6-35.2 T/750-1500 MHz for H-1) the O-17 quadrupolar and chemical shift parameters were determined for the two oxygen sites of each FMOC-protected amino acids and the three distinct oxygen environments of the dipeptide. The one- and two-dimensional, O-17, N-15-O-17, C-13-O-17, and H-1-O-17 double-resonance correlation experiments performed on the uniformly C-13,N-15 and 70% O-17-labeled dipeptide prove the attainability of O-17 as a probe for structure studies of biological systems. N-15-O-17 and C-13-O-17 distances were measured via one-dimensional REAPDOR and ZF-TEDOR experimental buildup curves and determined to be within 15% of previously reported distances, thus demonstrating the use of O-17 NMR to quantitate interatomic distances in a fully labeled dipeptide. Through-space hydrogen bonding of N-Ac-VL was investigated by a two-dimensional H-1-detected O-17 R-3-R-INEPT experiment, furthering the importance of O-17 for studies of structure in biomolecular solids.